Provenance is essential in scientific experiments. It contains information that is key to preserving the data and to determine it's quality and authorship. In complex experiments and analyses, where multiple tools are used to derive data products, provenance captured by these tools must be combined in order to determine the complete lineage of the derived products. We propose a mediator-based architecture to integrate provenance information from multiple sources, which contains two key components: a global mediated schema that is general and capable of representing provenance information represented in different models; and an expressive query interface that supports complex queries over provenance information spread over multiple different sources. We also present a case study where we show how this model was applied to integrate provenance from three provenance-enabled systems.